Tensor to Scalar Ratio in Non-Minimal $\phi^4$ Inflation

TL;DR

This paper analyzes non-minimal b4^4 inflation with gravitational coupling, showing it can fit observational data for tensor-to-scalar ratio and spectral index within certain parameter ranges, unlike minimal models.

Contribution

It demonstrates that non-minimal b4^4 inflation models can produce observationally consistent tensor-to-scalar ratios and spectral indices, extending previous minimal model predictions.

Findings

Predictions for r and n_s fit WMAP bounds for specific b4 and b4 coupling ranges.

Non-minimal b4^4 inflation can satisfy observational constraints, unlike minimal models.

Lower bound r > 0.002 for n_s > 0.96, considering quantum corrections.

Abstract

We reconsider non-minimal \lambda \phi^4 chaotic inflation which includes the gravitational coupling term \xi \mathcal{R} \phi^2, where \phi denotes a gauge singlet inflaton field and \mathcal{R} is the Ricci scalar. For \xi >> 1 we require, following recent discussions, that the energy scale \lambda^{1/4} m_P / \sqrt{\xi} for inflation should not exceed the effective UV cut-off scale m_P / \xi, where m_P denotes the reduced Planck scale. The predictions for the tensor to scalar ratio r and the scalar spectral index n_s are found to lie within the WMAP 1-\sigma bounds for 10^{-12} < \lambda < 10^{-4} and 10^{-3} < \xi < 10^2. In contrast, the corresponding predictions of minimal \lambda \phi^4 chaotic inflation lie outside the WMAP 2-\sigma bounds. We also find that r > 0.002, provided the scalar spectral index n_s > 0.96. In estimating the lower bound on r we take into account possible modifications due to quantum corrections of the tree level inflationary potential.